1. Field of the Invention
This invention relates to an air grease gun, more particularly to an air grease gun in which grease is in a pneumatic manner.
2. Description of the Related Art
The improvement of this invention is directed to a conventional air grease gun which is shown in FIG. 1. As illustrated, the conventional air grease gun includes a grip member 11, a coupler pipe 12 screwed to the front end or the grip member 11, a grease discharge pipe 13 coupled with the front end of the coupler pipe 12 by means of a fitting 131, and a grease storage tube 14 threaded to the internally threaded lower end portion 121 of the coupler pipe 12. A bottom cover 143 is removably mounted on the lower end of the grease storage tube 14. A longitudinal guide rod 144 is mounted removably in the central portion of the grease storage tube 14 and can be removed from the same by actuation of a rotary wheel 145. A trigger 16 is installed on the grip member 11 so as to open or close a trigger-controlled valve 17 which is disposed in the grip 11. A valve spring 17 biases the valve 17 to close the air passage 112. As illustrated, the grip 11 and the coupler pipe 12 define therebetween an interior chamber 111, (see FIG. 2) in which a barrel piston 150, a piston rod 151 integral with the barrel piston 150, and a barrel spring 152 are contained.
Referring to FIG. 2, the grip 1100 has an air passage 112 formed therethrough in communication with the interior chamber 111. which is formed with an inlet 113 that accepts compressed air from a compressed air source (not shown). The valve 17 normally closes the air passage 112. The trigger 16 can be actuated to move the valve 17 to the right so as to open the air passage 112, thus permitting compressed air to flow from the compressed air source into the interior chamber 111 via the air passage 112.
The hollow barrel 1500 of the gun is coupled with the grip 1100 and includes a diameter-reduced grease outlet portion 153 located at the front end portion thereof, and a partition 154 having a central hole and secured in the barrel 1500, in such a manner that a grease-tight seal is established between the peripheral wall of the barrel 1500 and the partition 154, so as to define a grease passage space 155 in front of the partition 154 in the barrel 1500. The barrel piston 150 is slidably mounted within the rear end portion of the barrel 1500 so as to define a rear air chamber 156 behind the partition 154 in the barrel 1500. The rear air chamber 156 is communicated with the air passage 112 of the grip 1100. The piston rod 151 is positioned in the barrel 1500 and has a front end portion extending through the central hole of the partition 154, and a rear end connected securely to the barrel piston 150. A grease-tight seal is established between the partition 154 and the piston rod 151. The barrel spring 152 is sleeved on the piston rod 151 in the barrel 1500 between the partition 154 and the barrel piston 150 so as to bias the barrel piston 150 to move rearward. A pressure relief device or a pressure relief opening 157 is formed through the peripheral wall of the barrel 1500 so as to relieve air pressure in the rear air chamber 156 of the barrel 1500 when increasing beyond a specified value so that the piston spring 152 can bias the barrel piston 150 to move rearward. The front end portion of the piston rod 151 can move into the diameter-reduced grease outlet portion 153 of the barrel 1500 so as to impel grease coming from the grease passage space 155 of the barrel 1500 into the fitting 131.
The grease discharge pipe 13 and the fitting 131 together constitute a spout pipe unit 1300 which is connected securely to the diameter-reduced grease outlet portion 153 of the barrel 1500 and which has a spout outlet 132 formed in the front end of the spout pipe unit 1300, and an interior bore 133 that is communicated with the grease passage space 155 of the barrel 1500. As best shown in FIG. 3, the interior bore 133 of the spout pipe unit 1300 has a large-diameter front section 134 and a small-diameter rear section 135 which is connected to and located just behind the large-diameter front section 134 and which has a diameter smaller than that of the large-diameter section 134. The sections 134 and 135 are located in the fitting 131. A ball 136 is accommodated in the large-diameter front section 134 of the fitting 131 and is biased by a ball spring 137 to close the front end of the small-diameter rear section 135 of the fitting 131, thereby preventing grease in the small-diameter rear section 135 from moving forward to the spout outlet 132 of the spout pipe 13 via the large-diameter front section 134 unless an additional force is applied to the same.
Again referring to FIG. 2, the vertical grease storage tube 14 has an externally threaded upper end portion 146 (see FIG. 1) coupled with the internally threaded lower end portion 121 of the coupler pipe 12. A horizontal tube piston 142 is slidably mounted within the grease storage tube 14 so as to define a grease storage chamber 148 above the tube piston 142, which is communicated with the grease passage space 155 of the barrel 1500. In use, as illustrated, a grease which is shaped in the form of a column is charged into the tube 14. As illustrated, the tube piston 142 has a central hole formed therethrough through which the guide rod 44 extends in such a manner that a grease-tight seal is established therebetween. A tube spring 147 pushes the tube piston 142 upward so as to move the grease in the grease storage chamber 148 into the grease passage space 155 of the barrel 1500. The ball spring 137 provides to the ball 136 a biasing force which is greater than upward biasing force of the tube spring 147 so that the grease fed from the tube 14 cannot pass beyond the ball 136. However, after long-term use, the ball spring 137 may become fatigued in terms of elasticity, thereby causing difficulties in feeding the grease from the tube 14 into the barrel 1500.